Zinc deficiency alters soybean susceptibility to pathogens and pests

Inadequate plant nutrition and biotic stress are key threats to current and future crop yields. Zinc (Zn) deficiency and toxicity in major crop plants have been documented, but there is limited information on how pathogen and pest damage may be affected by differing plant Zn levels. In our study, we used soybean plants as a host, a soybean pest, and three soybean pathogens to determine whether plant Zn levels change pest and disease assessments. Two soybean cultivars were grown in sand culture with a soluble nutrient solution that ranged from Zn-deficient to toxic. Detached leaves from these plants were either inoculated with Aphis glycines, the soybean aphid, Xanthomonas axonopodis pv. glycines, a bacterium that causes bacterial pustule, Sclerotinia sclerotiorum, the necrotrophic fungus responsible for stem rot, or Phakopsora pachyrhizi, a biotrophic obligate pathogen that causes soybean rust. There were significant (P < 5%) effects on aphid colonization, positive counts for bacterial pustule, S. sclerotiorum leaf area affected, and numbers of rust lesions associated with the Zn treatments. Plants grown with the physiologically optimal levels of Zn (2 mu M) had less (P < 5%) soybean aphids cm(-2) leaflet than plants grown without Zn, at 0.1 x Zn (0.2 mu M), or at 100x Zn fertilization (200 mu M). Plants grown with the normal fertilization of Zn or 100x Zn had fewer (P < 5%) positive counts for bacterial pustule and less lesion area affected by S. sclerotiorum than plants grown without Zn or fertilized with 0.1x Zn. For soybean rust, plants grown with the physiologically optimal fertilization of Zn or 100x Zn had higher (P < 5%) lesions cm(-2) on leaflets from plants grown without Zn or fertilized with 0.1x Zn. These results indicate different Zn nutrition levels in soybean significantly affected aphid and disease development.